1. Field of the Invention
The present invention relates to A/D converters, and more particularly, to a semiconductor chip with a number of A/D converters that include a group of redundant A/D converters.
2. Description of the Related Art
Medical ultrasound devices commonly utilize a processing unit, a head that is passed over a region to be imaged, and a cable that connects the head to the processing unit. The head, in turn, typically includes a row of piezoelectric transducing elements that send ultrasonic vibrations into the region to be imaged, and receive ultrasonic vibrations back from the region after the vibrations have bounced off of internal structures within the region.
The clarity of an ultrasonic image is proportional to the number of piezoelectric transducing elements that are used in a row of transducing elements. As a result, the industry is moving to increase the number of piezoelectric transducing elements that are used in a row, along with increasing the number of rows of piezoelectric transducing elements that are used in a head.
One of the difficulties of increasing the number of piezoelectric transducing elements is that each piezoelectric transducing element has a corresponding signal processing path. Conventionally, the signal processing path includes a low noise amplifier (LNA), a variable gain amplifier (VGA), and an analog-to-digital (A/D) converter.
Thus, if an ultrasonic device includes 256 piezoelectric transducing elements in one or more rows, then the ultrasonic device also includes 256 LNAs, 256 VGAs, and 256 A/D converters that form 256 individual signal processing paths. 256 A/D converters, however, is a large number of A/D converters.
Current-generation devices aggregate eight A/D converters onto one semiconductor chip. However, one problem with aggregating A/D converters onto a single chip is that the manufacturing yield goes down as the number of A/D converters on a single chip goes up. This is because each A/D converter has a large number of parameters, such as signal-to-noise ratio, that must meet the requirements of a specification.
Thus, if any one of these parameters on any one of the A/D converters is out of range (fails to meet specification), then the entire chip must be discarded. For example, if a semiconductor chip has eight A/D converters that each has 10 specification parameters that must be met, then a failure in any one of the 80 parameters will cause the entire chip to be discarded. If 16 A/D converters were aggregated onto a single chip, then a failure in any one of the 160 parameters will cause the entire chip to be discarded.
Thus, as the number of aggregated A/D converters increases, the number of parameters increases which, in turn, increases the likelihood that one of the parameters will be out of range (fail to meet specification). As noted above, failure to meet one of the specification requirements causes the entire chip to be discarded, thereby reducing the manufacturing yield.
As a result, there is a need for an approach to aggregating a large number of A/D converters onto a single chip that substantially increases the manufacturing yield.